binman: Tidy up pylint warnings in comp_util

Tweak some naming and comments to resolve these. Use WriteFile() to write
the file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/ftest.py b/tools/binman/ftest.py
index 90d7c3c..779b899 100644
--- a/tools/binman/ftest.py
+++ b/tools/binman/ftest.py
@@ -1927,7 +1927,7 @@
             self._ResetDtbs()
 
     def _decompress(self, data):
-        return comp_util.Decompress(data, 'lz4')
+        return comp_util.decompress(data, 'lz4')
 
     def testCompress(self):
         """Test compression of blobs"""
@@ -2806,7 +2806,7 @@
     def testExtractCbfsRaw(self):
         """Test extracting CBFS compressed data without decompressing it"""
         data = self._RunExtractCmd('section/cbfs/u-boot-dtb', decomp=False)
-        dtb = comp_util.Decompress(data, 'lzma', with_header=False)
+        dtb = comp_util.decompress(data, 'lzma', with_header=False)
         self.assertEqual(EXTRACT_DTB_SIZE, len(dtb))
 
     def testExtractBadEntry(self):
@@ -4233,13 +4233,13 @@
 
         # Check compressed data
         section1 = self._decompress(rest)
-        expect1 = comp_util.Compress(COMPRESS_DATA + U_BOOT_DATA, 'lz4')
+        expect1 = comp_util.compress(COMPRESS_DATA + U_BOOT_DATA, 'lz4')
         self.assertEquals(expect1, rest[:len(expect1)])
         self.assertEquals(COMPRESS_DATA + U_BOOT_DATA, section1)
         rest1 = rest[len(expect1):]
 
         section2 = self._decompress(rest1)
-        expect2 = comp_util.Compress(COMPRESS_DATA + COMPRESS_DATA, 'lz4')
+        expect2 = comp_util.compress(COMPRESS_DATA + COMPRESS_DATA, 'lz4')
         self.assertEquals(expect2, rest1[:len(expect2)])
         self.assertEquals(COMPRESS_DATA + COMPRESS_DATA, section2)
         rest2 = rest1[len(expect2):]